Rotational grip twist machine and method for fabricating bulges of twisted wire electrical connectors

ABSTRACT

Bulges in a wire having helically coiled strands are formed by untwisting the strands in an anti-helical direction at a predetermined position, to form an electrical connector from a length of the stranded wire. The wire is gripped by moving two spaced apart clamp members to a closed position and thereafter rotating the clamp members relative to one another in at least one complete relative revolution in a direction which is anti-helical relative to the coiled strands to form the bulge. The wire is gripped and rotated in the anti-helical direction for a relative rotational interval of greater than one-half, and preferably three-fourths, of a complete relative revolution. Thereafter, during the remaining rotational interval of each relative revolution, the clamp members are opened to permit the wire to be advanced to the next position where a bulge is to be formed.

CROSS-REFERENCE TO RELATED INVENTIONS

[0001] This invention is related to inventions for High-Speed,High-Capacity Twist Pin Connector Fabricating Machine and Method, WireFeed Mechanism and Method Used for Fabricating Electrical Connectors,and Pneumatic Inductor and Method of Electrical Connector Delivery andOrganization, described in the concurrently-filed U.S. patentapplications Ser. Nos. 190.326; 190.327; and 190.329, respectively, allof which are assigned to the assignee hereof, and all of which have atleast one common inventor with the present application. The disclosuresof these concurrently filed applications are incorporated herein by thisreference.

FIELD OF THE INVENTION

[0002] This invention generally relates to the fabrication of electricalinterconnectors used to electrically connect printed circuit boards andother electrical components in a vertical or z-axis direction to formthree-dimensional electronic modules. More particularly, the presentinvention relates to a new and improved machine and method forfabricating z-axis interconnectors of the type formed from helicallycoiled strands of wire, in which at least one longitudinal segment ofthe coiled strands is untwisted in an anti-helical direction to expandthe strands of wire into a resilient bulge. Bulges of the interconnectorare then inserted into vias of vertically stacked printed circuit boardsto establish an electrical connection through the z-axis interconnectorbetween the printed circuit boards of the three dimensional module.

BACKGROUND OF THE INVENTION

[0003] The evolution of computer and electronic systems has demandedever-increasing levels of performance. In most regards, the increasedperformance has been achieved by electronic components ofever-decreasing physical size. The diminished size itself has beenresponsible for some level of increased performance because of thereduced lengths of the paths through which the signals must travelbetween separate components of the systems. Reduced length signal pathsallow the electronic components to switch at higher frequencies andreduce the latency of the signal conduction through relatively longerpaths. One technique of reducing the size of the electronic componentsis to condense or diminish the space between the electronic components.Diminished size also allows more components to be included in a system,which is another technique of achieving increased performance because ofthe increased number of components.

[0004] One particularly effective approach to condensing the sizebetween electronic components is to attach multiple semiconductorintegrated circuits or “chips” on printed circuit boards, and then stackmultiple printed circuit boards to form a three-dimensionalconfiguration or module. Electrical interconnectors are then extendedvertically, in the z-axis dimension, between the printed circuit boardswhich are oriented in the horizontal x-axis and y-axis dimensions. Thez-axis interconnectors, in conjunction with conductor traces of eachprinted circuit board, connect the chips of the module with short signalpaths for efficient functionality. The relatively high concentration ofchips, which are connected by the three-dimensional, relatively shortlength signal paths, are capable of achieving very high levels offunctionality.

[0005] The vertical electrical connections between the stacked printedcircuit boards are established by using z-axis interconnectors. Z-axisinterconnectors contact and extend through plated through holes or“vias” formed in each of the printed circuit boards. The chips of eachprinted circuit board are connected to the vias by conductor tracesformed on or within each printed circuit board. The vias are formed ineach individual printed circuit board of the three-dimensional modulesat the same locations, so that when the printed circuit boards arestacked in the three-dimensional module, the vias of all of the printedcircuit boards are aligned vertically in the z-axis. The z-axisinterconnectors are then inserted vertically through the aligned vias toestablish an electrical contact and connection between the verticallyoriented vias of each module.

[0006] Because of differences between the individual chips on eachprinted circuit board and the necessity to electrically interconnect tothe chips of each module in a three-dimensional sense, it is not alwaysrequired that the z-axis interconnectors electrically connect to thevias of each printed circuit board. Instead, those vias on those circuitboards for which no electrical connection is desired are not connectedto the traces of that printed circuit board. In other words, the via isformed but not connected to any of the components on that printedcircuit board. When the z-axis interconnector is inserted through such avia, a mechanical connection is established, but no electricalconnection to the other components of the printed circuit board is made.Alternatively, each of the z-axis interconnectors may have thecapability of selectively contacting or not contacting each via throughwhich the interconnector extends. Not contacting a via results in noelectrical connection at that via. Of course, no mechanical connectionexists at that via either, in this example.

[0007] A number of different types of z-axis interconnectors have beenproposed. One particularly advantageous type of z-axis interconnector isknown as a “twist pin.” Twist pin z-axis interconnectors are describedin U.S. Pat. Nos. 5,014,419, 5,064,192, and 5,112,232, all of which areassigned to the assignee hereof.

[0008] An example of a prior art twist pin 50 is shown in FIG. 1. Thetwist pin 50 is formed from a length of wire 52 which has been formedconventionally by helically coiling a number of outer strands 54 arounda center core strand 56 in a planetary manner, as shown in FIG. 2. Atselected positions along the length of the wire 52, a bulge 58 is formedby untwisting the outer strands 54 in a reverse or anti-helicaldirection. As a result of untwisting the strands 54 in the anti-helicaldirection, the space consumed by the outer strands 54 increases, causingthe outer strands 54 to bend or expand outward from the center strand 56and create a larger diameter for the bulge 58 than the diameter of theregular stranded wire 52. The laterally outward extent of the bulge 58is illustrated in FIG. 3, compared to FIG. 2.

[0009] The strands 54 and 56 of the wire 52 are preferably formed fromberyllium copper. The beryllium copper provides necessary mechanicalcharacteristics to maintain the shape of the wire in the strandedconfiguration, to allow the outer strands 54 to bend outward at eachbulge 58 when untwisted, and to cause the bulges 58 to apply resilientradial contact force on the vias of the printed circuit boards. Tofacilitate and enhance these mechanical properties, the twist pin willtypically be heat treated after it has been fabricated. Heat treatinganneals or hardens the beryllium copper slightly and tempers the strands54 at the bulges 58, causing enhanced resiliency or spring-likecharacteristics. It is also typical to plate the fabricated twist pinwith an outer coating of gold. The gold plating establishes a goodelectrical connection with the vias. To cause the gold-plated exteriorcoating to adhere to the twist pin 50, usually the beryllium copper isfirst plated with a layer of nickel, and the gold is plated on top ofthe nickel layer. The nickel layer adheres very well to the berylliumcopper, and the gold adheres very well to the nickel.

[0010] The bulges 58 are positioned at selected predetermined distancesalong the length of the wire 52 to contact the vias 60 in printedcircuit boards 62 of a three-dimensional module 64, as shown in FIG. 4.Contact of the bulge 58 with the vias 60 is established by pulling thetwist pin 50 through an aligned vertical column of vias 60 in the module64. The outer strands 54 of the wire 52 have sufficient resiliency whendeflected into the outward protruding bulge 58, to resiliently pressagainst an inner surface of a sidewall 66 of each via 60, and therebyestablish the electrical connection between the twist pin 50 and the via60, as shown in FIG. 5. In those circumstances where an electricalconnection is not desired between the twist pin 50 and the components ofa printed circuit board, the via 60 is formed but no conductive tracesconnect the via to the other components of the printed circuit board.One such via 60′ is shown in FIG. 4. The sidewall 66 of the via 60′extends through the printed circuit board, but the via 60′ iselectrically isolated from the other components on that printed circuitboard because no traces extend beyond the sidewall 66. Inserting a bulge58 of the twist pin 50 into a via 60′ that is not connected to the othercomponents of a printed circuit board eliminates an electricalconnection from that twist pin to that printed circuit board, butestablishes a mechanical connection between the twist pin and theprinted circuit board which helps support and hold the printed circuitboard in the three-dimensional module.

[0011] To insert the twist pins 50 into the vertically aligned vias 60of the module 64 with the bulges 58 contacting the inner surfaces 66 ofthe vias 60, a leader 68 of the regularly-coiled strands 54 and 56extends at one end of the twist pin 50. The strands 54 and 56 at aterminal end 70 of the leader 68 have been welded or fused together toform a rounded end configuration 70 to facilitate insertion of the twistpin 50 through the column of vertically aligned vias. The leader 68 isof sufficient length to extend through all of the vertically alignedvias 60 of the assembled stacked printed circuit boards 62, before thefirst bulge 58 makes contact with the outermost via 60 of the outermostprinted circuit board 62. The leader 68 is gripped and the twist pin 50is pulled through the vertically aligned vias 60 until the bulges 58 arealigned and in contact with the vias 60 of the stacked printed circuitboards. To position the bulges in contact with the vertically alignedvias, the leading bulges 58 will be pulled into and out of some of thevertically aligned vias until the twist pin 50 arrives at its finaldesired location. The resiliency of the strands 54 allow the bulges 58to move in and out of the vias without losing their ability to makesound electrical contact with the sidewall of the final desired via intowhich the bulges 58 are positioned. Once appropriately positioned, theleader 68 is cut off so that the finished length of the twist pin 50 isapproximately at the same level or slightly beyond the outer surface ofthe outer printed circuit board of the module 64. A tail 72 at the otherend of the twist pin 50 extends a shorter distance beyond the last bulge58. The strands 54 and 56 at an end 74 of the tail 72 are also fusedtogether. The length of the tail 72 positions the end 74 at a similarposition to the location where the leader 68 was cut on the oppositeside of the module. However, if desired, the length of the tail 72 orthe remaining length of the leader 68 after it was cut may be madelonger or shorter. Allowing the tail 72 and the remaining portion of theleader 68 to extend slightly beyond the outer printed circuit boards 62of the module 64 facilitates gripping the twist pin 50 when removing itfrom the module 64 to repair or replace any defective components. Inthose circumstances where it is preferred that the ends of the twist pindo not extend beyond the outside edges of the three-dimensional module,an overlay may be attached to the outermost printed circuit boards tomake the ends of the twist pin flush with the overlay.

[0012] The ability to achieve good electrical connections between thevias 60 of the printed circuit boards depends on the ability toprecisely position the location of the bulges 58 along the length ofwire 52. Otherwise, the bulges 58 would be misaligned relative to theposition of the vias, and possibly not create an adequate electricalconnection. Therefore, it is important in the formation of the twistpins 50 that the bulges 58 be separated by predetermined intervals 76(FIG. 1) along the length of the wire 52. The position of the bulges 58and the length of the intervals 76 depend on the desired spacing betweenthe printed circuit boards 62 of the module 64. The amount of bending ofeach of the outer conductors 54 at each bulge 58 must also be controlledso that each of the bulges 58 exercises enough force to make goodelectrical contact with the vias. Moreover, the amount of outwarddeflection or bulging of each of the bulges 58 must be approximatelyuniform so that none of the bulges 58 experiences permanent deformationwhen the bulge is pulled through the vias. Distortion-induceddisparities in the dimensions of the bulges adversely affect theirability to make sound electrical connections with the vias 60. Furtherstill, each twist pin 50 should retain a coaxial configuration along itslength without slight angular bends at each bulge and without any bulgehaving asymmetrical characteristics. The coaxial configurationfacilitates inserting the twist pin through the vertically aligned vias,maintaining the resiliency of the bulges, and establishing goodelectrical contact with the vias.

[0013] The requirements for close tolerances and precision in the twistpins are made more significant upon recognizing the very small size ofthe twist pins. The typical sizes of the most common sizes ofhelically-coiled wire are about 0.0016, 0.0033 and 0.0050 in. indiameter. The diameters of the strands 54 and 56 used in forming thesethree sizes of wires are 0.005, 0.0010, and 0.0015 in., respectively.The typical length of a twist pin having four to six bulges whichextends through four to six printed circuit boards will be about 1 to1.5 inches. The outer diameter of each bulge 58 will be approximatelytwo to three times the diameter of the regularly stranded wire in theintervals 76. The tolerance for locating the bulges 58 between intervals76 is in the neighborhood of 0.002 in. The weight of a typicalfour-bulge twist pin is about 0.0077 grams, making it so light thathandling the twist pin is very difficult. Handling each twist pin isalso complicated because its small dimensions do not easily resist theforces that are necessary to manually manipulate the twist pin withoutbending or deforming it. It is not unusual that a complex 4 in.×4 in.module 64 may require the use of as many as 22,000 twist pins. Thus, therelatively large number of twist pins necessary to assemble eachthree-dimensional module require an ability to fabricate a relativelylarge number of the twist pins in an efficient and rapid manner.

[0014] A general technique for fabricating twist pins is described inthe three previously-identified U.S. patents. That described techniqueinvolves advancing the length of the stranded wire, clamping thestranded wire above and below the location where the bulge is to beformed, fusing the outer strands of the wire to the core strand of thewire preferably by laser welding at the locations above and below thebulge, and rotating the wire between the two clamps in an anti-helicaldirection to form the bulge.

[0015] In a prior art implementation of this twist pin fabricationtechnique, a wire feeder advanced an end of the helically stranded wirewhich was wound on a spool. The wire feeder employed a lead screwmechanism driven by an electric motor to advance the wire and unwind itfrom the spool. A solenoid-controlled clamp was connected to the leadscrew mechanism to grip the wire as the lead screw mechanism advanced asmuch of the stranded wire from the spool as was necessary for use ateach stage of fabrication of the twist pin. To advance more wire, theclamp opened and the lead screw mechanism retracted in a reversemovement. The clamp then closed again on the wire and the electric motoragain advanced the lead screw mechanism.

[0016] While this prior art wire feeder mechanism was functional, thereciprocating movement of the feeder mechanism reduced efficiency andslowed the speed of operation. Half of the reciprocating movement, thereturn movement to the beginning position, was wasted motion. Moreover,the relatively high inertia and mass of the lead screw, clamp and motorarmature required extra force and hence time to execute the reversingmovements necessary for reciprocation. Furthermore, the rotational massof the wire wound on the spool limited the acceleration rate at whichthe lead screw could unwind the wire off of the spool. The rotationalmass was frequently sufficient enough to cause the wire to slip in theclamp carried by the lead screw. Slippage at this location resulted inthe formation of the bulges at incorrect positions and incorrect lengthsof the leader 68 and the internal lengths 76. The desire to avoidslippage also limited the operating speed of the fabricating equipment.

[0017] The prior art bulge forming mechanism included two clampingdevices which closed on the wire above and below at the location whereeach bulge was to be formed. The clamping devices held a wire while alaser beam fused the outer strands 54 to the center core strand 56 atthose locations. Thereafter, the lower clamping device was rotated in ananti-helical direction while the upper clamping device held the wirestationary, thereby forming the bulge 58.

[0018] The lower clamping device was carried by a sprocket, and the wireextended through a hole in the center of the sprocket. A first pneumaticcylinder was connected to the clamping device to cause the clampingdevice to grip the wire. A chain extended around the sprocket and meshedwith the teeth of the sprocket. One end of the chain was connected to aspring, and the other end of the chain was connected to a secondpneumatic cylinder. When the second pneumatic cylinder was actuated, itsrod and piston pulled the chain to rotate the sprocket by the amount ofthe piston throw. Upon reaching the end of its throw, the rod andcylinder of the second pneumatic cylinder was returned in the oppositedirection to its original position by the force of the spring whichpulled the chain in the opposite direction. Of course, moving the chainto its original position also rotated the sprocket in the oppositedirection to its original position.

[0019] After gripping the wire by activating the first pneumaticcylinder, the second pneumatic cylinder was activated to rotate thesprocket in the anti-helical direction. However, the throw of the secondpneumatic cylinder, and the amount of rotation of the sprocket, wasinsufficient to completely form a bulge with a single rotationalmovement. Instead, two of separate rotational movements were required tocompletely form the bulge. After the rotation, the lower clamping devicereleased its grip on the wire while the sprocket rotated in the reversedirection. Upon rotating back to the initial position again, the lowerclamping device again gripped the wire and another rotational movementof the sprocket and gripping device was executed to finish forming thebulge.

[0020] By providing only a limited amount of rotational movement so asto require two rotations to form the bulge, a significant amount of timewas consumed in forming each bulge. The latency of reversing themovement of the components and executing multiple bulge formingmovements slowed the fabrication rate of the twist pins. The rotationalmass of the sprocket and the clamping mechanism with its attachedsolenoid activation clamping device reduced the rate at which theseelements could be accelerated, and also constituted a limitation on thespeed at which twist pins could be fabricated. Apart from the rotationalmass issues, acceleration had to be limited to avoid inducing wireslippage. The need to reverse the direction of movement of numerousreciprocating components limited the rate at which the twist pins bulgescould be fabricated.

[0021] After formation of the bulges in the prior art twist pinfabricating machine, the wire with the formed bulges was cut to lengthto form the twist pin. The leader of the twist pin extended into aventuri through which gas flowed. The effect of the gas flowing throughthe venturi was to induce a slight tension force on the wire, and holdit while a laser beam severed the wire at the desired length. The laserbeam fused the ends 70 and 74 of the strands 54 and 56 as it severed thefabricated twist pin from the length of wire. The tension force inducedon the wire by the gas flowing through the venturi propelled the twistpins into a random pile called a “haystack.” After a sufficient numberof twist pins had accumulated, they were placed into a separate sortingand singulating machine which ultimately delivered the twist pins one ata time in a specific orientation into a carrier. The pins were laterheat treated and transferred from the carrier and inserted into thethree-dimensional modules.

[0022] The process of sorting the twist pins, orienting them, deliveringthem into the carrier, and making sure that the twist pins were receivedproperly within the carrier required considerable human intervention andmachine handling after the twist pins were fabricated. Occasionally thetwist pins would be lodged in tubes which guided the twist pins into thecarrier by an air flow. Delivering the twist pins into the receptaclesin the carrier was also difficult, and human intervention was requiredto assure that the twist pins were properly received in the receptacles.Twist pin sorting also occasionally resulted in jamming and bending thetwist pins. In general, the post-fabrication processing steps requiredto organize the twist pins for their subsequent use contributed tooverall inefficiency.

[0023] These and other considerations pertinent to the fabrication oftwist pins have given rise to the new and improved aspects of thepresent invention.

SUMMARY OF THE INVENTION

[0024] One improved aspect of the present invention involves formingbulges in helically coiled wire in the such manner that allows twistpins to be more rapidly and more efficiently fabricated compared toprevious techniques. Another improved aspect of the present inventioninvolves fabricating twist pins having more uniform, more controlled,more precisely positioned and more symmetrically shaped bulges. Anotherimproved aspect of the present invention involves fabricating bulges andtwist pins without using reciprocal motions. The lost motion of returnstrokes and the latency associated with reciprocation decreases thespeed of fabricating the twist pins. The necessity to acceleraterelatively massive components is avoided by using continuous movementsor intermittent movements which do not involve changes of direction andwhich tend to conserve energy and momentum without requiringacceleration of massive components. Another improved aspect is that wireslippage is avoided during the fabrication of the bulges. Other aspectsof the present invention allow the bulges and twist pins of differentsizes to be fabricated conveniently using the same machine.

[0025] In one principal regard, the present invention relates to a bulgeforming mechanism for forming bulges in a wire having helically coiledstrands by untwisting the strands in an anti-helical direction at apredetermined position to form an electrical connector from a segment ofa length of the wire. The bulge forming mechanism includes a firstgripping assembly including a first clamp member and a first actuator.The first clamp member moves to a closed position to grip the wire andprevent the wire from moving relative to it and moves to an openposition in which the wire is free to move relative to it. The firstactuator selectively moves the first clamp member into the open andclosed positions. The bulge forming mechanism also includes a secondgripping assembly which includes a second clamp member and secondactuator. The second clamp member moves to a closed position to grip thewire and prevent the wire from moving relative to it and moves to anopen position in which the wire is free to move relative to the secondclamp member. The second actuator selectively moves the second clampmember into the open and closed positions. A rotating carrierinterconnects the first and second gripping assemblies to rotate thefirst and second clamp members relative to one another in at least onecomplete relative revolution in a single relative rotational directionwhich is anti-helical relative to the strands of the wire, therebyforming the bulge. The first and second clamp members spaced above andbelow the location where the bulge is formed.

[0026] In another principal regard, the present invention relates to amethod of forming bulges in a wire having helically coiled strands byuntwisting the strands in an anti-helical direction at a predeterminedposition to form an electrical connector from a length of the wire. Themethod comprises the steps of gripping the wire with a first clampmember and preventing the wire from moving relative to the first clampmember by moving the first clamp member to a closed position, grippingthe wire with a second clamp member and preventing the wire from movingrelative to the second clamp member by moving the second clamp member toa closed position, positioning the first and second clamp members atspaced apart locations above and below the location where a bulge is tobe formed, rotating the first and second clamp members relative to oneanother in at least one complete relative revolution in a relativerotational direction which is anti-helical relative to the strands ofthe wire, and moving the first and second clamp members to the closedposition during a relative rotational interval of greater than one-halfof a complete relative revolution of the clamp members.

[0027] Preferably, the first and second clamp members are moved to theclosed position during a relative rotational interval of approximatelythree-fourths of a complete relative revolution. Preferably the firstand second clamp members are moved to the open position to release thegrip on the wire and to allow the wire to move relative to the clampmembers during a relative rotational interval of less than one-half of acomplete relative revolution of the clamp members. While both clampmembers are in the open position, the wire is advanced longitudinally toestablish the next position to form a bulge or to establish a positionwhere the segment of wire is severed from the remaining wire. While theclamp members are in the open position, the relative rotation of theclamp members may be slowed, stopped or otherwise controlled to providesufficient time for advancing the wire, if necessary or desired.

[0028] A preferred technique of avoiding wire slippage involvesrepositioning the strands of the wire into a cross-sectionalconfiguration having a radial component when gripping the strands. Atleast one of the clamp members includes jaw members with crescent shapedcontact surfaces which reposition the strands into the cross-sectionalconfiguration having the radial component. The radial component of thecross-sectional configuration allows more torque to be applied to thewire without slippage.

[0029] In a preferred embodiment, the first clamp member is retained ina stationary position and the second clamp member is rotated in completerevolutions in a single rotational direction relative to the first clampmember. The second clamp member is moved to the open and closedpositions at predetermined points during each revolution. The secondactuator preferably includes a cam wheel which has at least oneactuating arm extending outward beyond a peripheral edge of the rotatingcarrier which carries the cam wheel. Rotation of the carrier brings theactuating arm into contact with a trip pin, and the continued rotationof the carrier with the actuating arm in contact with a trip pin rotatesthe cam wheel. As the cam wheel rotates, an eccentric surface of the camwheel pivots a lever arm of the second clamp member to move the secondclamp member into the open and closed positions. Preferably at least twoactuator arms and two trip pins are located to open and close the secondclamp member at the predetermined positions during each of itsrevolutions. The second clamp member preferably includes a pair ofseparated lever arms between which the cam wheel and its cam surfacesare positioned to pivot the lever arms in a further separated conditionto open the second clamp member and to allow the lever arms toresiliently move back to a normal less-separated position to close thesecond clamp member.

[0030] The first clamp member is preferably moved to the closed positionby an electrical actuator, which is triggered by a sensor which sensesthe position of the actuator arms of the cam wheel of the secondactuator. The first clamp member is normally resilient to move to theopen position. By independently actuating the movements of the clampmembers, their open and closed positions may be controlled independentlyof the open and closed positions of the second rotating clamp member.The clamp members are preferably formed of spring tempered material toachieve the normal open and closed positions and to create inherent biasforce when the clamp members are deflected.

[0031] The relative rotation of the clamp members in completerevolutions allows a bulge to be formed during a relative rotationalinterval of less than one complete revolution. Multiple incompletemovements in the anti-helical direction are avoided when forming eachbulge. The single bulge-forming movement results in twist bulges whichhave more uniform and symmetrical characteristics. The rotationalinterval during which the clamp members are open allows the bulges to bemore precisely located along the segment of wire and allows the ends ofthe segment to be accurately positions for severing. As a result, thetwist pin has more consistent dimensions and characteristics, becausethe single rotational movement of creating each bulge is less likely toinduce bends or other characteristics in the twist pin which make itnon-coaxial along its length. The continual relative rotational movementof the clamp members allows the twist pins to be fabricated withoutincurring the inefficient lost motion and the latency associated withreciprocal motions, thereby increasing the speed and efficiency offabricating the twist pins. The necessity to accelerate relativelymassive components is avoided by using the continuous relativerotational movements which do not involve changes of direction and whichconserve energy and momentum without requiring changes of direction andsubstantial acceleration of massive components. These improvements areachieved while still allowing twist pins of different sizes anddimensions to be fabricated.

[0032] A more complete appreciation of the present invention and itsscope may be obtained from the accompanying drawings, which are brieflysummarized below, from the following detailed descriptions of presentlypreferred embodiments of the invention, and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a side elevational view of a prior art twist pin.

[0034]FIG. 2 is an enlarged, cross-sectional view of the twist pin shownin FIG. 1, taken substantially in the plane of line 2-2 shown in FIG. 1.

[0035]FIG. 3 is an enlarged, cross-sectional view of the twist pin shownin FIG. 1, taken substantially in the plane of line 3-3 shown in FIG. 1.

[0036]FIG. 4 is a partial, vertical cross-sectional view of a prior artthree-dimensional module, formed by multiple printed circuit boards andillustrating a single twist pin of the type shown in FIG. 1 extendingthrough vertically aligned vias of the printed circuit boards of themodule.

[0037]FIG. 5 is an enlarged cross-sectional view of the twist pin withina via shown in FIG. 4, taken substantially in the plane of line 5-5shown in FIG. 4.

[0038]FIG. 6 is a perspective view of a machine for fabricating twistpins of the type shown in FIG. 1, in accordance with the presentinvention.

[0039]FIG. 7 is an enlarged perspective view of a wire feed mechanism, abulge forming mechanism, an inductor mechanism and a portion of a twistpin receiving mechanism of the twist pin fabricating machine shown inFIG. 6.

[0040]FIG. 8 is an enlarged, perspective view of the bulge formingmechanism shown separated from the other components shown in FIGS. 6 and7, with certain components not shown for purposes of clarity.

[0041]FIG. 9 is an enlarged, exploded perspective view of a stationarygripping assembly and a rotating gripping assembly of the bulge formingmechanism shown in FIG. 8.

[0042]FIG. 10 is an exploded, perspective view of the rotating grippingassembly of the bulge forming mechanism shown in FIG. 9.

[0043]FIG. 11 is an enlarged top plan view of the stationary grippingassembly shown in FIGS. 8 and 9.

[0044]FIG. 12 is an enlargement of that portion of FIG. 11 generallybounded by lines 12-12, illustrating jaw members of a stationary clampmember of the stationary gripping assembly shown in FIG. 11.

[0045]FIG. 13 is a section view taken substantially in the plane of line13-13 shown in FIG. 12.

[0046]FIG. 14 is an illustration similar to FIG. 12, but illustratinggripping the wire by the jaw members shown in FIG. 12.

[0047]FIG. 15 is an illustration similar to FIG. 14, but illustratingreleasing the wire by the jaw members shown in FIG. 12.

[0048]FIG. 16 is a top plan view of the rotating gripping assembly shownin FIG. 9 and other portions of the bulge forming mechanism, with arotating clamp member of the rotating gripping assembly removed forpurposes of illustration.

[0049]FIG. 17 is a top plan view similar to that shown in FIG. 10, butincluding the rotating clamp member of the rotating gripping assembly,with portions broken away for purposes of illustration.

[0050]FIG. 18 is an enlargement of a portion of FIG. 17 bounded by lines18-18, illustrating jaw members of a rotating clamp member of therotating gripping assembly shown in FIG. 17.

[0051]FIG. 19 is a section view taken substantially in the plane of line19-19 shown in FIG. 18.

[0052]FIG. 20 is an illustration similar to FIG. 19, but illustratinggripping the wire by the jaw members shown in FIG. 18.

[0053]FIG. 21 is an illustration similar to FIG. 20, but illustratingreleasing the wire by the jaw members shown in FIG. 18.

[0054] FIGS. 22-24 are illustrations of portions of the rotatinggripping assembly shown in FIGS. 8, 9, and 17, illustrating sequentialoperation while forming a bulge of the twist pin shown in FIG. 1.

[0055]FIG. 25 is a flowchart of the basic methodology of forming bulgeswhile fabricating twist pins according to the present invention and ofthe functions performed by the twist pin fabricating machine shown inFIG. 6.

DETAILED DESCRIPTION

[0056] The present invention is preferably incorporated in an improvedmachine 100 which fabricates twist pins 50 (FIG. 1), and in improvedmethodology for fabricating bulges 58 (FIG. 1) of twist pins, as shownand understood by reference to FIG. 6. The twist pins are fabricatedfrom the gold-plated, beryllium-copper wire 52 which is wound on a spool102. A wire feed mechanism 104 of the machine 100 unwinds the wire 52from the spool 102 and accurately feeds the wire to a bulge formingmechanism 106 which is located below the wire feed mechanism 104. Thebulge forming mechanism forms the bulges 58 (FIG. 1) at preciselocations along the length of the wire 52. The positions where thebulges 58 are formed is established by the advancement of the wire 52 bythe wire feed mechanism 104. The bulge forming mechanism 106 forms thebulges by gripping the wire 52 and untwisting the wire in the reverse oranti-helical direction.

[0057] After all of the bulges of the twist pin 50 (FIG. 1) have beenformed by the bulge forming mechanism 106, the wire feed mechanism 104advances the twist pin configuration formed in the wire 52 into apneumatic inductor mechanism 108. With the twist pin positioned in theinductor mechanism 108, the end 74 of the tail 72 or the end 70 of theleader 68 (FIG. 1) of the twist pin configuration is located below thebulge forming mechanism 106. A laser beam device 110 is activated andits emitted laser beam melts the wire 52 at the ends 70 and 74 (FIG. 1),thus completing the formation of the twist pin 50 by severing thefabricated twist pin from the remaining wire 52.

[0058] The severed twist pin is released into the pneumatic inductormechanism 108. The inductor mechanism 108 applies a slightly negativerelative gas or air pressure or suction to the twist pin, and creates agas flow which conveys the severed twist pin downward through a tube 112of a twist pin receiving mechanism 114. The twist pin receivingmechanism 114 includes a cassette 116 into which receptacles 118 areformed in a vertically oriented manner. The tube 112 of the inductormechanism 108 delivers one twist pin into each of the receptacles 118.Once a twist pin occupies one of the receptacles 118, an x-y movementtable 120 moves the cassette 116 to position an unoccupied receptacle118 beneath the tube 112. The x-y movement table 120 continues movingthe cassette 116 in this manner until all of the receptacles 118 havebeen filled with fabricated twist pins. Once the cassette 116 has beenfilled with twist pins, the filled cassette is removed and replaced withan empty cassette, whereupon the process continues. Later after heattreatment, the fabricated twist pins are removed from the cassette 116and inserted into the vias 60 to form the three-dimensional module 64(FIG. 4).

[0059] The operation of the wire feed mechanism 104, the bulge formingmechanism 106, the inductor mechanism 108, the laser beam device 110 andthe twist pin receiving mechanism 114 are all controlled by a machinemicrocontroller or microcomputer (referred to as a “controller,” notshown) which has been programmed to cause these devices to execute thedescribed functions. The spool 102, the wire feed mechanism 104, thebulge forming mechanism 106, the inductor mechanism 108 and the laserbeam device 110 are interconnected and attached to a first frame element122. A support plate 124 extends vertically upward from the first frameelement 122, and the wire feed mechanism 104, the bulge formingmechanism 106 and the inductor mechanism 108 are all connected to orsupported from the support plate 124. The twist pin receiving mechanism114 is connected to a second frame element 126. Both frame elements 122and 126 are connected rigidly to a single structural support frame (notshown) for the entire machine 100. All of the components shown anddescribed in connection with FIG. 6 are enclosed within a housing (notshown).

[0060] More details concerning the twist pin fabricating machine 100 andmethod of fabricating twist pins are described in the above-referencedand concurrently-filed U.S. patent application, Ser. No. 190.326.Specific details concerning the wire feed mechanism 104 are described inthe above-referenced and concurrently-filed U.S. patent application,Ser. No. 190.327. However, some of the more specific but neverthelessgeneral details of the wire feed mechanism 104 are next described ascontext for the present invention.

[0061] As shown in FIGS. 6 and 7, the wire feed mechanism 104 includes apre-feed electric motor 150 that rotates a connected, speed-reducinggear head 151. A capstan 152 is connected to and rotated by the gearhead 151. The wire 52 extends between the capstan 152 and an adjacentidler roller 154. The outer surfaces of the capstan 152 and the roller154 apply sufficient frictional force on the wire 52 to firmly grip thewire between the capstan 152 and the roller 154 and to advance the wirewithout slippage when the capstan 152 is rotated. Rotating the capstan152 to advance the wire 52 also unwinds wire 52 from the spool 102.

[0062] The rotating capstan 152 advances the wire 52 into a cavity 170.A front transparent door 176 covers the cavity 170. Vertically extendingcontact bars 178 and 180 are positioned on the opposite lateral sides ofthe cavity 170. A cavity exit guide 186 is located at the bottom of thecavity 170. An exit hole extends vertically downward through the cavityguide 186 at a position which is directly vertically below the contactpoint of the pre-feed capstan 152 and the roller 154 and directly abovethe point where the wire 52 enters the bulge forming mechanism 106.

[0063] The wire 52 is withdrawn from the cavity 170 by rotating a wirefeed spindle 200. A precision feed motor 212 is connected to rotate thespindle 200. A pinch roller 220 is biased toward the spindle 200 toestablish good frictional contact of the wire 52 between the spindle 200and the pinch roller 220 to precisely advance the wire 52 by an amountdetermined by the rotation of the precision feed motor 212.

[0064] The wire is withdrawn or unwound from the spool by operating thepre-feed motor 150 and pre-feed capstan 152 independently of operatingthe precision feed motor 212 and the spindle 200. A slack amount of wireis accumulated in the cavity 170 as an S-shaped configuration 234. TheS-shaped configuration 234 consumes enough slack wire within the cavityto form at least one twist pin. The slack wire of the S-shapedconfiguration 234 is not under tension or resistance from the spool 102(FIG. 6), thereby allowing the wire 52 to be advanced precisely from thecavity 170 into the bulge forming mechanism 106 by the precision feedmotor 212 and the spindle 200. The slack amount of wire consumed by theS-shaped configuration 234 in the cavity 170 exhibits very littleinertia and mass, thereby allowing the precision feed motor 212 andspindle 200 to advance a desired amount of wire quickly, without havingto overcome the adverse influences of attempting to accelerate asignificant mass of wire, accelerate the rotation of the spool 102, orto overcome significant inertia of the wire on the spool and the spoolwhile unwinding the wire. The effects of high mass under highacceleration conditions, and the effects of inertia, can induce slippagein the wire as it is advanced under high speed manufacturing conditions,thereby resulting in forming the bulges 58 at incorrect positions and inundesired lengths of the leader 68, the tail 72 and the interval 76 ofthe twist pin 50 (FIG. 1).

[0065] As the wire in the cavity 170 is fed out by the precision feedmotor 212 and spindle 200, the pre-feed motor 150 and the capstan 152feed more wire into the cavity to maintain the S-shaped configuration234. The pre-feed motor 150 is energized and operates to advance wirefrom the spool into the cavity until bends of the S-shaped configuration234 contact the contact bars 178 and 180. When the bends of the S-shapedconfiguration 234 contact both contact bars 178 and 180, the power tothe pre-feed motor 150 is terminated. Thereafter, as the precision feedmotor 212 and spindle 200 withdraw wire from the cavity 170, causing theS-shaped configuration 234 to become narrower and withdraw the bends ofthe S-shaped configuration from the contact bars 178 and 180, power isagain supplied to the pre-feed motor 150 to advance more wire into thecavity 170 until the S-shaped configuration is re-established.

[0066] The precision feed motor 212 is preferably a conventional steppermotor. As such, the times of its rotation and the extent of its rotationare precisely controlled by pulse signals which cause the stepper motor212 to rotate in a predetermined increment of a full rotation for eachpulse delivered. For example, one pulse might cause the stepper motor212 to rotate one rotational increment or one degree. A predeterminednumber of rotational increments are required to cause the motor 212 torotate one complete revolution. Moreover, the stepper motor 212 respondsby advancing through the rotational increment very rapidly in responseto the delivery of each pulse. Consequently, there is very little timelatency between the delivery of each pulse to the stepper motor 212 andthe increment of rotation achieved by that pulse. The fractional amountof one revolution of the spindle 200 is directly related to the amountof linear advancement of the wire 52 by the spindle 200. By recognizingthese relationships, the amount of wire 52 advanced by the spindle 200is precisely controlled by delivering a predetermined number of pulsesto the stepper motor 212 which will result in the advancement of thewire 52 by a linear amount which correlates to the predetermined numberof pulses delivered to the stepper motor 212.

[0067] For example, if the relationship is such that one pulse to thestepper motor will result in the advancement of the wire by 0.001 inch,the advancement of the wire by ¼ of an inch (0.250 inch) is achieved byapplying 250 pulses to the stepper motor. The position of the wire isalso achieved in a similar manner. As another example in which one pulseto the stepper motor will result in the advancement of the wire by 0.001inch, if it is desired to space the bulges 58 apart from one anotheralong the twist pin 50 by an interval 76 (FIG. 1) of {fraction (1/10)}of an inch (0.100 inch) and the length consumed by each bulge 58 is{fraction (2/10)} of an inch (0.200 inch), the wire 52 is advanced by{fraction (3/10)} of an inch to form the sequential bulges by applying300 pulses to the stepper motor 212.

[0068] Because of the relatively rapid response and accelerationcharacteristics of the stepper motor 212, the stepper motor 212 iscapable of advancing the wire 52 very rapidly. Thus, the stepper motor212 offers the advantages of precise amounts of advancement of the wire52, precise positioning of the wire 52 during the formation of thebulges 58, and positioning and advancement of the wire on a very rapidbasis.

[0069] In forming the twist pin 50, the number of pulses delivered tothe stepper motor 212 is calculated to correlate to the desiredposition, the desired amount of advancement and hence the length of thewire 52 into the bulge forming mechanism 106 to create the desiredlength of the leader 68, to create the desired amount of interval 76between the bulges 58, and to create the desired length of the tail 72at the location where the wire 52 is severed after the formation of thetwist pin 50. As is discussed below in conjunction with the bulgeforming mechanism 106, the delivery of the calculated number of pulsesis also timed to coincide with operational states of the bulge formingmechanism 106, thus assuring that the wire is advanced to the calculatedextent at the appropriate time to coincide with the proper operationalstate of the bulge forming mechanism 106. Details concerning theimproved bulge forming mechanism 106 and an improved method offabricating bulges in a helically coiled wire in accordance with thepresent invention are described below.

[0070] As shown in FIGS. 6-10, the bulge forming mechanism 106 comprisesa stationary gripping assembly 290, a rotating gripping assembly 292 anda drive motor 294 connected by a timing belt 296 to the rotatinggripping assembly 292. The drive motor 294 applies rotational forcethrough the belt 296 to rotate the rotating gripping assembly 292. Thewire 52 is advanced from the feed wire mechanism 104 through astationary clamp member 298 of the stationary gripping assembly 290 andthrough a rotating clamp member 300 of the rotating clamp assembly 292.The stationary clamp member 298 and the rotating clamp member 300 openapproximately simultaneously to allow the wire 52 to be advanced. Bothclamp members 298 and 300 thereafter close approximately simultaneouslyto grip the wire 52.

[0071] The stationary clamp member 298 closes around the wire 52 withsufficient force to restrain the wire 52 against rotation. The rotatingclamp member 300 also closes around the wire 52 with sufficient force tohold the wire 52 stationary with respect to the rotating clamp member300. However, because the rotating clamp member 300 is rotating due tothe rotational energy applied by the drive motor 294 to the rotatinggripping assembly 292, the stationary grip of the wire 52 by therotating clamp member 300 rotates the wire 52 between the clampingmembers 298 and 300 in the opposite or anti-helical direction comparedto the direction that the strands 54 have been initially wound aroundthe core strand 56 (FIG. 1). As a result of the reverse or anti-helicalrotation imparted by the rotating gripping assembly 292, one bulge 58 isformed between the rotating clamp member 300 and the stationary clampmember 298.

[0072] After formation of the bulge 58, both clamp members 298 and 300are again opened, and the wire feed mechanism 104 advances the wire 52to position the wire at a predetermined position along the length of thewire 52 where the next bulge 58 (FIG. 1) will be formed. The rotatingclamp member 300 opens sufficiently wide so that the expanded width ofthe bulge 58 will pass through the opened rotating clamp member 300.

[0073] As shown in FIG. 14, the rotating gripping assembly 292 isconnected to a mounting bracket 302, and a mounting bracket 302 isconnected to the support plate 124 of the machine 100 (FIG. 7). Thedrive motor 294 is connected to a mounting plate 304 which is attachedto the support plate 124 by a bracket 306 (FIG. 7). The belt 296 extendsthrough an opening (not shown) in the support plate 124. The rotatinggripping assembly 292 is mounted on a base plate 308, and the base plate308 is connected to the mounting bracket 302. As shown in FIG. 10, allof the components of the rotating gripping assembly 292 are connecteddirectly or indirectly to the base plate 308.

[0074] The stationary gripping assembly 290 is also connected to thebase plate 308 by a mounting block 310, as shown on FIGS. 8 and 11. Thestationary clamp member 298 is connected to the mounting block 310.Preferably the stationary clamp member 298 is formed from a relativelythin sheet of spring tempered steel. A base portion 312 of thestationary clamp member 298 is connected by screws 314 and a reinforcingstrip 316 to the mounting block 310. As shown in FIG. 11, the baseportion 312 is relatively wide and therefore offers considerabletorsional resistance to bending or flexing at the location where thestationary clamp member 298 is connected to the mounting block 310. Anarcuate portion 318 of the stationary clamp member 298 extends in asemi-circular curve from the base portion 312. The arcuate portion 318is defined by a cylindrical hole 320 formed through the clamp member298. An arm portion 322 extends from the arcuate portion 318.

[0075] The base portion 312 and the arm portion 322 are separated fromone another at a separation which is defined by parting edges 324 and326 of the base portion 312 and the arm portion 322, respectively.Because of the separation defined by the parting edges 324 and 326, thearm portion 322 is able to pivot slightly inward (clockwise as shown inFIG. 11) to further close the parting edges 324 and 326. The slightinward pivoting movement of the arm portion 322 with respect to the baseportion 312 occurs as a result of slightly deflecting the arcuateportion 318. However, the torsional resistance of the arcuate portion318 tends to resist such slight pivoting movement, and the torsionalresistance of the arcuate portion 318 forces the arm portion 322 toreturn to its original position in which the parting edges 324 and 326are slightly separated as shown in FIG. 11.

[0076] A solenoid 330 is connected by a bracket 331 to the base plate308. A plunger 332 extends from the solenoid 330, and a forward end 334of the plunger 332 is pivotally connected to an outer end 336 of the armportion 322. When electrical current this applied to the solenoid 330,the plunger 332 is pulled into the solenoid 330 and applies force on theouter end 336 of the arm portion 322. In response to the force from thesolenoid, the arm portion 322 pivots slightly (clockwise as shown inFIG. 11) against the torsional resistance of the arcuate portion 318,and causes the parting edges 324 and 326 to come closer together. Themovement of the parting edges 324 and 326 toward one another closes thestationary clamp member 298, to grip the wire 52 (FIG. 14). Whenelectrical current flow to the solenoid 330 is terminated, the torsionalresistance of the arcuate portion 318 permits the arm portion 322 toreturn back to its original position, thereby withdrawing the plunger332 from within the solenoid 330. When the solenoid 330 does not causethe plunger to pivot the arm portion 322, the gripping surfaces 350 and352 are separated sufficiently to allow the wire to advance between them(FIG. 15).

[0077] Jaw members 340 and 342 are formed on the parting edges 324 and326, respectively, as shown in FIG. 12. Shoulders 344 and 346 of the jawmembers 340 and 342 face each other, but the shoulders 344 and 346 avoidcontacting one another by a separation tolerance 348. Semicirculargripping surfaces 350 and 352 are formed in a facing relationship in theshoulders 344 and 346, respectively. The semicircular shape of thegripping surfaces 350 and 352 is established to apply a radial inwardforce on all of the planetary strands 54, to firmly pinch thoseplanetary strands 54 against the center core strand 56 of the wire 52,as shown in FIG. 14. The force from the solenoid 330 overcomes thetorsional resistance characteristics of the arcuate portion 318 of thestationary clamping member 298 to force the jaw members 340 and 342toward one another (FIG. 14). When the planetary strands 54 are pinchedagainst the core strand 56 as shown in FIG. 14, the separation tolerance348 is less than before the solenoid 330 was energized (as is understoodby comparing the dimension 348 in FIGS. 12 and 14). In somecircumstances, the shoulders 344 and 346 may touch one another to reducethe tolerance 348 to zero. As a result of the decreased separationtolerance 348 and the curvature of the gripping surfaces 350 and 352,the amount of gripping force on the wire 52 derived from the solenoid330 is sufficient to prevent the wire from slipping in rotation aroundthe gripping surfaces 350 and 352 when the bulge 58 is formed from therotation of the rotating gripping assembly 292.

[0078] When the solenoid 330 is not activated, the jaw members 340 and342 move away from one another and thereby open the stationary clampmember 298, and the amount of the separation tolerance 348 returns tonormal as shown in FIGS. 12 and 15. The normal amount of tolerance 348as shown in FIG. 15 offers sufficient clearance to allow the wire 52 toadvance without excessive dragging. However, because the jaw member 340is part of the stationary base portion 312 of the stationary clampmember 298, the gripping surface 350 does not move as does the grippingsurface 352 on the jaw member 342. The gripping surface 350 is alsopositioned in direct coaxial alignment with the location where the wireis fed from the wire feed mechanism. Consequently, as the wire 52 isadvanced while the stationary clamp member 298 is open (FIG. 15) thewire 52 lightly contacts the jaw member 340 at its gripping surface 350.This contact establishes electrical potential reference on the wirewhich is used by the wire feed mechanism 104 in connection with thecontact bars 178 and 180 (FIG. 7) to control the formation of theS-shaped configuration in the manner described above.

[0079] The size of the gripping surfaces 350 and 352 must be adjusted toaccommodate different sizes of wire 52. The wire size adjustment isaccomplished by replacing the stationary clamp member 298 with a similarclamp member 298 having different sized gripping surfaces 350 and 352.The semicircular gripping surface 350 of the stationary clamp member 298should be aligned very precisely in a coaxial position with respect tothe center line of the wire 52 advanced from the wire feed mechanism 104and the rotational center of the rotating gripping assembly 292.Otherwise, the bulges 58 formed by the rotating gripping assembly 292will be laterally displaced from the axis of the wire 52, the bulges maybe non-symmetrical, and the fabricated twist pin may be slightly bent.Laterally displaced and non-symmetrical bulges and slight bends in thetwist pin can cause problems when transporting the fabricated twist pinsthrough the inductor mechanism 108 and into the twist pin receivingmechanism 114 (FIG. 6). The position of the gripping surfaces 350 and352 relative to the rotational center of the bulge forming mechanism 106is adjusted by loosening the screws 314 (FIG. 9) and adjusting theposition of the stationary clamp member 298 on the mounting block 310until the gripping surfaces 350 and 352 are precisely located, at whichtime the screws 314 may be tightened.

[0080] The stationary clamp member 298 is preferably formed from a sheetof conventional spring tempered steel. The size and configuration of thejaw members 340 and 342, the shoulders 344 and 346, and the grippingsurfaces 350 and 352 are established by conventional electricaldischarge machining (EDM).

[0081] As shown in FIGS. 9 and 10, a pulley wheel 370 forms thefoundational rotational component of the rotating gripping assembly 292.The pulley wheel 370 is connected by bearings 374 and 376 to a post 372which extends from the base plate 308. The outer circumference of thepulley wheel 370 is configured with teeth 378 which mesh withcorresponding teeth 380 of the timing belt 296. Of course, a similartoothed pulley wheel (not shown) is connected to the drive motor 294(FIG. 8) and the teeth of that other tooth pulley also mesh with theteeth 380 of the belt 296 to rotate the pulley wheel 370. The drivemotor 294 is a conventional stepper motor. The number and frequency ofpulses delivered to the stepper drive motor 294 control its rotationalposition and rotational rate in a conventional manner. The use of thetoothed timing belt 296 to rotate the pulley wheel 370 permits precisecontrol over the rotational rate and position of the pulley wheel 370and the other elements of the rotating gripping assembly 292 carried bythe pulley wheel 370.

[0082] A carrier disk 382 is attached to the upper surface of the pulleywheel 370 by screws (not shown). An outside peripheral orcircumferential edge 383 of the carrier disk 382 extends slightly beyondthe periphery of the teeth 378 to form a ridge for confining the belt296 to the pulley wheel 370. A relatively wide rectangular groove 385extends completely diametrically across the carrier disk 382, as is alsoshown in FIG. 16. The rotating clamp member 300 and its associatedcomponents are located within the groove 385. A semicircular recess 384is formed in the groove 385 adjacent to the peripheral edge of thecarrier disk 382. A cam wheel 386 is positioned within the recess 384.The cam wheel 386 includes a center shaft 388 from which four outwardlyprotruding actuating arms 390, 392, 394 and 396 extend. As shown in FIG.16, the actuating arms 390, 392, 394 and 396 extend at 90 degreerotational intervals from one another around the center shaft 388.

[0083] A cam member 398 is attached to the actuating arms 390-396surrounding the center shaft 388. The cam member 398 has a first curvedsurface 400 which is generally radially aligned with the first actuatingarm 390. On the diametrically opposite side of the cam member 398, asecond curved surface 402 is generally radially aligned with the secondactuating arm 394. The curved surfaces 400 and 402 each have an arcuateshape that extends at the same radial distance from the axial center ofthe center shaft 388. First and second flat surfaces 404 and 406,respectively are also formed on the cam member 398. The flat surfaces404 and 406 extend tangentially with respect to a diametric referenceextending through the axial center of the center shaft 388. The firstflat surface 404 is generally radially aligned with the second actuatingarm 392, and a second flat surface 406 is generally radially alignedwith the fourth actuating arm 396.

[0084] The bottom end of the center shaft 388 fits within a cylindricalhole 408 formed in the carrier disk 382, as shown in FIG. 10. With thebottom end of the center shaft 388 in the hole 408, the cam wheel 386 isable to rotate relative to the carrier disk 382. The circumference ofthe recess 384 is slightly beyond the outer extremities of the actuatingarms 390-396 to allow the actuating arms 390-396 to rotate freely withinthe recess 384 without contacting any portion of the carrier disk 382.However, because the hole 408 and the center shaft 388 are positionedclosely adjacent to the outer circumferential edge of the carrier disk382, the actuating arms 390-396 are able to rotate into a position inwhich one of the actuating arms 390-396 extends radially outward beyondthe outer peripheral edge 383 of the carrier disk 382, as shown in FIGS.9,16 and 17.

[0085] The upper end of the center shaft 388 extends into a similarlyshaped circumferential hole 410 formed in a cover plate 412, as shown inFIG. 10. The cover plate 412 is attached to the carrier disk 382 byscrews (not shown). In addition to covering the cam wheel 386 andsupporting the upper end of its center shaft 388, the cover 412 alsocovers the rotating clamp member 300 and elements which connect it tothe carrier disk 382. A hole 413 is formed in the center of the coverplate 412. The wire 52 is delivered to the rotating gripping assembly292 through the hole 413.

[0086] The rotating clamp member 300 is connected to the carrier disk382 by a slide member 414 which fits within a radially extending slot416 of the rectangular groove 385, as shown in FIGS. 10 and 16. The slot416 extends radially outward on one side of the carrier disk 382 at agenerally diametrically opposite location from the location where therecess 384 extends radially outward on the opposite side of the carrierdisk 382. A pin 418 fits within a hole 420 of the slide member 414. Thepin 418 also fits within a hole 422 (FIG. 10) of the rotating clampmember 300 to hold the rotating clamp member 300 on the carrier disk382.

[0087] The position of the slide member 414 on the carrier disk 382, andhence the position of the rotating clamp member 300 on the carrier disk382, is adjusted by eccentric pins 424 and 426. A cylindrical shaftbottom portion of the eccentric pin 424 fits within a cylindrical hole428 formed in the carrier disk 382 in the slot 416. A top end portion ofthe pin 424 fits within a hole 430 formed in the slide member 414. Thetop end portion of the pin 424 is eccentrically-positioned with respectto the cylindrical shaft bottom portion of the pin 424. Consequently,rotating the pin 424 with a screwdriver inserted in at a slot formed inthe top end portion of the pin 424 adjusts the radial position of theslide member 414 within the slot 416.

[0088] In a similar manner, a lower cylindrical shaft portion of theeccentric pin 426 fits within a cylindrical hole 432 in the carrier disk382. A top portion of the eccentric pin 426 is aneccentrically-positioned with respect to the lower shaft portion. Theupper portion of the eccentric pin 426 passes through a slot 434 formedin an inner end of the slide member 414. Rotation of the eccentric pin426 with a screwdriver placed in the slot in its upper portion causesthe slide member 414 to pivot about the eccentric pin 424, therebyadjusting the circumferential or tangential position of the pin 418extending from the slide member 414.

[0089] The rotating clamp member 300 is formed from a flat piece ofresilient spring tempered steel. The clamp member 300 includes agenerally circular end portion 450 into which a circular slot 452 hasbeen formed to create two arcuate portions 454 and 456, as shown inFIGS. 10 and 17. The arcuate portions 454 and 456 extend from a positionnear the hole 422 into which the pin 418 from the slide member 414extends. The circular slot 452 also defines an inner circular portion458 into which a hole 460 and a slot 462 are formed. The hole 460 andthe slot 462 are positioned above the eccentric pins 424 and 426,respectively. The holes 460 and the slot 462 permit a screwdriver to beinserted into the slots of the eccentric pins 424 and 426, to rotate thepins and adjust the position of the rotating clamp member 300 on thecarrier disk 382 as previously described.

[0090] Lever arm portions 464 and 466 extend from the arcuate portions454 and 456, respectively, in a generally parallel, bifurcated manner.Inner edges 468 and 470 of the lever arm portions 464 and 466,respectively, are positioned on opposite sides of the cam member 398 ofthe cam wheel 386. The lever arm portions 464 and 466 are separated fromone another near the center of the rotating clamp member 300 at partingedges 472 and 474. The parting edges 472 and 474 face one another, andthe wire 52 extends between the parting edges 472 and 474.

[0091] Jaw members 476 and 478 are formed on the parting edges 472 and474 as shown in FIG. 18. Shoulders 480 and 482 of the jaw members 476and 478 face each other and normally contact each other thereby causinga separation tolerance 484 between the shoulders 480 and 482 to be veryslight or non-existent. Crescent shaped gripping surfaces 486 and 488are formed in a facing relationship in the shoulders 480 and 482,respectively. The jaw members 476 and 478 are undercut in the areas 490and 492 below the crescent shaped gripping surfaces 486 and 488,respectively, to reduce the vertical area of the gripping surfaces 486and 488, as shown in FIG. 19. The reduced vertical area of the grippingsurfaces 486 and 488 concentrates the force applied by the grippingsurfaces 486 and 488 on the wire.

[0092] The crescent shape of the gripping surfaces 486 and 488 pushesthe strands 54 and 56 of the wire 52 into an oval configuration as shownin FIG. 20, when the wire is gripped. The oval configuration of thestrands 54 and 56 creates a radial dimension (horizontally, as shown inFIG. 20) to the configuration of the strands 54 and 56 when they arepinched together by the gripping surfaces 486 and 488. The radialdimension of the oval configuration permits the gripping surfaces 486and 488 to apply more torque to the wire while untwisting the strands 56to form the bulge 58 (FIG. 1). The oval configuration of the strands 54and 56 is more effective in resisting rotational slippage when the bulgeis created than a circular configuration of the gripping surfaces.

[0093] In general, the crescent shaped curvature of the grippingsurfaces 486 and 488 should create a football shape surrounding the wirewhen it is gripped (FIG. 20). The maximum width between the grippingsurfaces 486 and 488 when no wire is present between them (FIG. 18)should be approximately one-half of the distance from the more pointed,displaced ends. Of course, the size of the gripping surfaces 486 and 488must be adjusted to accommodate different sizes of wire 52. The wiresize adjustment is accomplished by replacing the rotating clamp member300 with a similar clamp member 300 having different sized grippingsurfaces 486 and 488. The rotating clamp member 300 is preferably formedfrom a sheet of conventional spring tempered steel. The configuration ofthe jaw members 476 and 478, the shoulders 480 and 482, and the grippingsurfaces 486 and 488 is formed by conventional electrical dischargemachining (EDM).

[0094] The gripping surfaces 486 and 488 should be aligned in a coaxialposition with respect to the center line of the wire 52 in the rotatinggripping assembly 292 and from the wire feed mechanism 104. Otherwise,the bulges 58 formed will be laterally displaced from the axis of thewire 52 and may also be non-symmetrical, or a slight bend in the wirewill be induced so that the twist pin will be bent out of coaxialalignment. Laterally displaced and non-symmetrical bulges, and twistpins which are slightly bent out of coaxial alignment, may causedelivery problems when transporting the fabricated twist pins throughthe inductor mechanism 108 and into the twist pin receiving mechanism114, as well as insertion problems when the twist pin is insertedthrough the printed circuit boards of the module.

[0095] The torsional force characteristics of the arcuate portions 454and 456 of the rotating clamp member 300 force the jaw members 476 and478 toward one another. When the strands 54 and 56 of the wire 52 arepinched as shown in FIG. 20, the separation tolerance 484 is greaterthan would occur under circumstances where no wire is pinched betweenthe gripping surfaces 486 and 488, as is understood by comparing FIGS.18 and 20. As a result of the increased separation tolerance 484 and thecrescent shaped curvature of the gripping surfaces 486 and 488 and theirreduced vertical surface area (FIG. 19), the amount of torque applied bythe arcuate portions 454 and 456 to the jaw members 476 and 478 issufficient to grip the wire so that the rotating gripping assembly 292can untwist the strands in the anti-helical direction to form the bulge58 (FIG. 1).

[0096] The rotating clamp member 300 develops the pinching force fromthe resiliency of the spring tempered steel from which the clamp member300 is formed. The resiliency of the material of the arcuate portions452 and 454 causes force which biases the lever arm portions 464 and 466toward one another, thereby pinching the strands 54 and 56 of wirebetween the gripping surfaces 486 and 488. Under such conditions, theflat surfaces 404 and 406 of the cam member 398 are located adjacent toand extend generally parallel to the inner edges 468 and 470 of thelever arm portions 464 and 466, as shown in FIG. 17. A slight tolerancebetween the flat surfaces 404 and 406 and the adjoining inner edges 468and 470 is typical when the wire is pinched between the grippingsurfaces 486 and 488, as shown in FIG. 19. When there is no wire pinchedbetween the gripping surfaces 486 and 488, the inner edges 468 and 470will typically contact the flat surfaces 404 and 406.

[0097] To separate the gripping surfaces 486 and 488, the cam wheel 386must be rotated to position the curved surfaces 400 and 402 of the cammember 398 into contact with the inner edges 468 and 470 of the leverarm portions 464 and 466. This condition is illustrated in FIG. 23. Thecurved surfaces 400 and 402 force the lever arm portions 464 and 466apart to separate the gripping surfaces 486 and 488 and release the wire52 located between those gripping surfaces. Moreover, the separation ofthe gripping surfaces 486 and 488 is sufficient to permit a bulge 58 topass between the separated gripping surfaces 486 and 488 as the wire isadvanced after the formation of the bulge, as shown in FIG. 21.

[0098] The cam wheel 386 is rotated as a result of the actuating arms390, 392, 394 and 396 contacting trip pins 500 and 502, as illustratedin FIGS. 22-24. The trip pins 500 and 502 are positioned in holes 504and 506, respectively, of a yoke member 508, as shown in FIGS. 9, 16,17and 22-24. The yoke member 508 is connected to a riser member 510, andthe riser member 510 is connected to the base plate 308 (FIG. 9). Thetrip pins 500 and 502 are positioned radially adjacent to the outercircumferential edge 383 of the carrier disk 382. The rotating carrierdisk 382 moves the cam wheel 386 in a circular path to contact theoutwardly extending one of actuating arms 390-396 with the trip pins 500and 502. When a radially outward extending actuating arm 390-396 comesinto contact with a trip pin 500 or 502, the continued rotation of thecarrier disk 382 causes the cam wheel 386 to rotate about its centershaft 388 by one-fourth of a complete revolution. The radially outwardextending actuating arm rotates rearwardly with respect to the directionof rotation of the carrier disk 382 into a position extending somewhattangentially to the outside peripheral edge 383 of the carrier disk 382,while the next actuating arm rotates into a position extending radiallyoutward so that it will contact the next trip pin encountered. In thismanner, each time an actuating arm contacts one of the trip pins 500 and502, the cam wheel 386 is rotated another one-fourth of a completerevolution.

[0099] A slot 512 (FIG. 9) extends through the yoke member 508 to permitthe actuating arms 390-396 to rotate and to pass through the yoke member508 without contacting any part of the yoke member 508 other than thetrip pins 500 and 502. The trip pins 500 and 502 are located at a 90degree relative rotational displacement from one another, as a shown inFIGS. 16, 17 and 22-24. The rotation of the cam wheel 386 is caused bythe sequence of the actuating arm 390 contacting the trip pin 500followed by the actuating arm 392 contacting the trip pin 502 during onerevolution of the rotating gripping assembly 292, followed in the nextrevolution of the rotating gripping assembly by the actuating arm 394contacting the trip pin 500 followed by the actuating arm 396 contactingthe trip pin 502. The rotation of the cam wheel 386 as a result of theseactuating arms contacting these trip pins causes the rotating clampmember 300 to grip the wire 52 during three-fourths or 270 degrees ofone complete revolution of the rotating gripping assembly 292 (whenrotating clockwise as shown in FIGS. 24 and 22 from pin 502 around topin 500) and to release the wire 52 during one-fourth or 90 degrees ofone complete revolution of the rotating gripping assembly 292 (whenrotating clockwise as shown in FIG. 23 from pin 500 to pin 502). Thebulge 58 (FIG. 1) is formed during the 270 degree rotation of therotating gripping assembly. The grip on the wire is released by therotating gripping assembly 292 and the wire is advanced by the wire feedmechanism 104 during the 90 degrees of rotation. This gripping androtating action of the rotating gripping assembly 292, to form the bulge58, is illustrated in FIGS. 22-24.

[0100] As shown in FIG. 22, the first actuator arm 390 is extendingradially outward beyond the circumferential edge 383 of the carrier disk382. The first flat surface 404 of the cam member 398 is adjacent andparallel to the inner edge 468 of the lever arm portion 464, and thesecond flat surface 406 is adjacent and parallel to the inner edge 470of the lever arm portion 466. The first actuating arm 390 is about tocontact the trip pin 500, due to the clockwise (as shown) rotation ofthe carrier disk 382. The function of the trip pin 500 is to rotate thecam wheel 386 to cause the rotating clamp member 300 to open and releasethe grip on the wire 52. As the disk carrier 382 rotates the cam wheel386 past the opening trip pin 500, the cam wheel 386 rotatescounterclockwise (as shown) to extend the first actuating arm 390 in arearward direction (relative to the clockwise rotational direction ofthe carrier disk 382 as shown) and to extend the second actuating arm392 radially outward, as shown in FIG. 23.

[0101] In the rotational condition shown in FIG. 23, the cam member 398has been rotated to position the second curved surface 402 in contactwith the inner edge 468 of the lever arm portion 464, and the firstcurved surface 400 has been positioned in contact with the inner edge470 of the lever arm portion 466. The curved surfaces 400 and 402 forcethe lever arm portions 464 and 466 apart, thereby increasing thedistance between the gripping surfaces 486 and 488 to release the wire.The separation of the gripping surfaces 486 and 488 and the release ofthe wire is shown in FIGS. 21 and 23. Thus, the opening trip pin 500causes the rotating clamp member 300 to release the grip on the wirewhen the carrier disk 382 rotates the cam wheel 386 into adjacency withthe opening trip pin 500.

[0102] After the wire has been released, which is the condition shown inFIGS. 21 and 23, the wire 52 remains released while the carrier member382 rotates until the second actuating arm 392 comes in contact with thetrip pin 502. The continued rotation of the carrier disk 382 with thesecond actuating arm 392 in contact with the trip pin 502 causes the camwheel 386 to rotate one-fourth of a revolution in the counterclockwisedirection, as shown in FIG. 24. The second actuating arm 392 pivotsrearwardly into a tangential position with respect to the outercircumferential edge 383 and the third actuating arm 394 extendsradially outward. With the third actuating arm 394 extending radiallyoutward, the second flat surface 406 is adjacent to the inner edge 468of the lever arm portion 464, and the first flat surface 404 is adjacentto the inner edge 470 of the lever arm portion 464. In this condition,the lever arm portions 464 and 466 are biased toward one another,causing the gripping surfaces 486 and 488 to again grip the wire 52 asshown in FIG. 20. Thus, the trip pin 502 causes the cam wheel 386 torotate into a position where the rotating clamp member 300 grips thewire, as shown in FIG. 24.

[0103] The rotating gripping assembly 292 rotates 270 degrees orthree-fourths of a revolution from the position shown in FIG. 24 to theposition shown in FIG. 22, and the sequence of events illustrated inFIGS. 22-24 thereafter repeats itself, except that the sequence startswith the third actuating arm 394 contacting the opening trip pin 500 andthe fourth actuating arm 396 contacting the closing trip pin 502.Because of the symmetric configuration of the cam wheel 386, there is arelative reversal of the positions of the curved surfaces 400 and 402and the flat surfaces 404 and 406 relative to the inner edges 368 and370 of the lever arm portions 464 and 466 during subsequent revolutionsof the carrier disk 382. This reversal of relative positionalrelationships occurs with every subsequent rotation of the carrier disk382 because the cam wheel 386 makes one revolution for each two completerevolutions of the carrier disk 382. Nevertheless, because of thesymmetric relationship of the cam wheel 386, the same operation occurswith each revolution of the rotating gripping assembly 292.

[0104] The closed, gripping condition of the clamp member 300 ismaintained during the 270 degrees of rotation of the cam wheel 386 fromthe closing trip pin 502 (position shown in FIG. 24) to the opening trippin 500 (position shown in FIG. 22). During this 270 degree rotationalinterval, the bulge is formed as a result of gripping the wire androtating the gripped wire in the anti-helical direction due to rotationof the rotating gripping assembly 292. The ability to untwist thestrands in the anti-helical direction in a single 270 degree rotationalinterval is a considerable improvement over prior devices which couldonly untwist the strands for less than 180 rotational degrees. As aresult of the present improvements, the bulge forming mechanism 106 iscapable of making one bulge with a single rotation of the rotatinggripping assembly 292, compared to the requirements of prior devices togrip, twist and release the wire at the location of the bulge two timesin order to fully develop the bulge.

[0105] During rotation of the cam wheel 386 from the opening trip pin500 (the position shown in FIG. 22) to the closing trip pin 502 (theposition shown in FIG. 24), the wire 52 is released and the grippingsurfaces 486 and 488 of the jaw members 476 and 478 of the rotatingclamp member 300 are opened (FIG. 21). During the time occupied inrotating the rotating gripping assembly 292 through the open interval of90 rotational degrees, the stationary and rotating clamp members 298 and300 must be opened approximately simultaneously. Opening the stationaryclamp member 298 is accomplished by de-energizing the solenoid 330(FIGS. 8, 9, 11) of the stationary gripping assembly 290, as previouslydescribed.

[0106] To coordinate the application of electrical energy to thesolenoid 330 with the mechanical opening of the rotating clamp member300, an opening sensor 514 (FIGS. 8, 9,16,17, 22-24) is attached to theyoke member 508 at a position to sense the presence of the actuatingarms 390 or 394 making contact with the opening trip pin 500. Preferablythe opening sensor 514 is a photoelectric sensor which delivers atrigger signal on a cable 516 (FIGS. 8 and 9) to the controller (notshown) of the machine 100. The machine controller responds to thetrigger signal to control the delivery of electrical energy to thesolenoid 330 through an electrical cable 518 (FIG. 8) and to activatethe precision feed motor 212 to rotate the spindle 200 (FIG. 7) toadvance the wire from the wire feed mechanism 104.

[0107] With both clamp members 298 and 300 in an open condition, thewire feed mechanism 104 advances the wire to the predetermined extentnecessary to position the wire for forming the bulges 58, the leader 68,the tail 72, and the intervals 76 between the bulges. The rotationalrate and position of the rotating gripping assembly 292 is preciselycontrolled by the timed delivery of pulses to the stepper drive motor294 during this interval to provide enough time for the wire to beadvanced. Consequently, the rotational speed of the rotating grippingassembly 292 can be controlled very closely during all portions of eachrevolution of the rotating gripping assembly 292. By slowing therotational rate of the rotating gripping assembly 292 during the 90degree rotational interval when the clamp members 298 and 300 are open,a relatively longer amount of wire can be advanced. Enough wire to formthe leader 68 (FIG. 1) of the twist pin 50 may be advanced under theseconditions, for example.

[0108] Closing the stationary clamp member 298 by the solenoid 330 isalso controlled from knowledge of the rotational position of therotating gripping assembly 292 resulting from the sensor 514 supplyingthe trigger signal. The number of pulses delivered to the stepper drivemotor 294 determines the rotational position that the rotating grippingassembly 292. When the number of pulses supplied to the drive motor 294positions the rotating gripping assembly 292 so that the actuator arms392 and 396 are about to contact with the closing pin 502, thecontroller of the machine 100 delivers current to the solenoid 330,thereby closing the stationary clamp member 298.

[0109] After the twist pin configuration has been formed in the wire, itis necessary to sever the twist pin configuration from the continuouswire in order to complete the fabrication of the twist pin. Under suchconditions, the wire is advanced until the end 70 of the leader 68 orthe end 74 of the tail 72 (FIG. 1) is in a position below the bulgeforming mechanism 106, as may be understood by reference to FIGS. 6 and7. The wire 52 is advanced by the wire feed mechanism 104 through thebulge forming mechanism 106 until a point on the wire is aligned withthe point where a laser beam will be trained onto the wire in a cuttingchamber 520 (FIGS. 6 and 7). The laser beam device 110 is thenactivated, and the energy from the laser beam severs the wire by meltingit into two pieces, thus forming an end 74 of the in tail 72 on onesevered piece and the end 70 of the leader 68 on the other severed piece(FIG. 1). Melting at the ends 70 and 74 fuses the strands 54 and 56together to simultaneously form the ends 70 and 74 (FIG. 1).

[0110] In the context of the present invention, it is desired that aslight tension be applied to the wire while it is severed. To create thetension, gas is delivered to the venturi assembly 540 (FIG. 7) whichinduces the tension on the wire as it is cut. The tension induced by theventuri assembly is resisted by the spindle 200 and the idler roller 220of the wire feed mechanism 104 (FIG. 7) which are non-rotational at thistime. The stationary gripping assembly 290 should also be closed toresist the tension created by the venturi assembly 540.

[0111] The severed twist pin whose fabrication has just been completedis removed by the inductor mechanism 108 and conveyed through the tube112 of the twist pinned receiving mechanism 114 and delivered into areceptacle 118 of the cassette 116 (FIGS. 6 and 7). More detailsconcerning the inductor mechanism 108 and the twist pin receivingmechanism 114 are described in the above-referenced andconcurrently-filed U.S. patent application Ser. No. 190.329.

[0112] The manner in which the above-described bulge forming mechanism106 functions in conjunction with the wire feed mechanism 104, and thegeneral method of fabricating bulges on the twist pins according to thepresent invention, is illustrated by a process flow shown at 700 in FIG.25. The separate operations of the machine and the steps of the methodin the process flow 700 are referenced by separate reference numbers.The process flow 700 presumes normal functionality without considerationof error or malfunction conditions.

[0113] The process flow 700 begins at step 702. At step 704, wire isunwound from the spool 102 and advanced into the cavity 170 of the wirefeed mechanism 104 (FIGS. 6, 7). Step 704 also involves forming andmaintaining the S-shaped configuration 234 (FIG. 7).

[0114] At step 706, the stationary gripping assembly 290 is closed (FIG.14) by energizing the solenoid 330 (FIGS. 11, 14). The rotating grippingassembly 294 (FIGS. 9,10) is rotated by energizing the stepper drivemotor 294 (FIG. 8), as shown at step 708. Next, as shown at step 710,the rotating gripping assembly is rotated until it reaches the positionat which the rotating gripping assembly is opened (FIG. 21) by thecontact of the actuating arm 390 or 394 with the opening trip pin 500(FIG. 22). Also as part of step 710, the stationary gripping assembly290 is opened (FIG. 15) as a result of de-energizing the solenoid 330(FIG. 11) in response to the trigger signal from the sensor 514.

[0115] With both the stationary and the rotating gripping assemblies inthe open position as a result of executing step 710, the wire is nextadvanced at step 712 as a result of energizing the precision feed motor212 with pulses to cause it to rotate the spindle 200 (FIG. 7). Therotating spindle 200 advances slack wire from the S-shaped configuration234 in the cavity 170 into the bulge forming mechanism 106 (FIG. 7). Thewire is advanced at step 712 until the desired location for forming thebulge 58 (FIG. 1) is established. The correct position of the wire isestablished by counting the number of energizing pulses applied to beprecision stepper motor 212.

[0116] Once the wire has been positioned at the desired location for theformation of a bulge, at step 712, the wire is gripped by closing boththe stationary and the rotating gripping assemblies, as shown at step714. Closing the stationary gripping assembly (FIG. 14) is achieved byenergizing the solenoid 300 (FIG. 11) at a time correlated to the numberof pulses supplied to the stepper drive motor 294 (FIGS. 7 and 8) sothat the stationary gripping assembly closes at approximately the sametime or slightly earlier than the rotating gripping assembly closes.Closing the rotating gripping assembly (FIG. 20) is achieved by rotationof the rotating gripping assembly 292 until one of the actuating arms392 or 396 contacts the closing trip pin 502 (FIG. 24). Upon executionof step 714, the wire 52 is gripped above and below the position where abulge 58 (FIG. 1) is to be formed.

[0117] A bulge 52 (FIG. 1) is thereafter formed during the rotation ofthe rotating gripping assembly 292 through the bulge-forming rotationalinterval, as shown at step 716. The bulge forming rotational interval isthat part of a complete revolution of the rotating gripping assemblyclockwise from the position shown in FIG. 24 to the position shown inFIG. 22. During this rotational interval, the bulge 58 (FIG. 1) isformed in a single continuous, uninterrupted movement by the action ofthe rotating gripping assembly 292.

[0118] At step 718, the stationary gripping assembly and the rotatinggripping assembly are both opened (FIGS. 15 and 21). The stationarygripping assembly is opened by de-energizing the solenoid 330 (FIG. 11)in response to the trigger signal supplied by the sensor 514. Therotating gripping assembly is opened by the contact of one of theactuating arms 590 or 594 with the opening trip pin 500 (FIG. 22).

[0119] A determination is thereafter made at step 720 as to whether thelast bulge of the twist pin has just been formed. If not, the programflow loops back to step 708, and thereafter steps at 708, 710, 712, 714,716, 718, and 720 are again executed in a loop. The steps of this loopare repeated, until all of the bulges 58 (FIG. 1) of the twist pin havebeen formed. Once all of the bulges for the twist pin have been formed,the determination at step 720 causes the program flow to advance to step722.

[0120] The rotating gripping mechanism is stopped or slowed at step 722.The rotational position where the rotating gripping mechanism is slowedor stopped is in that part of the rotational interval where the rotatinggripping assembly 292 is opened (FIG. 23), after an actuating arm 390 or394 of the cam wheel 386 has contacted the open trip pin 500 (FIG. 22).Slowing or stopping the rotating gripping mechanism in the part of itsrotational interval where the rotating gripping assembly is opened isachieved by controlling the application of energizing pulses to thestepper drive motor 294 (FIG. 8).

[0121] Executing steps 718 and 722 allows the wire to be advanced atstep 724. The wire advancement at step 724 positions the wire at alocation where ends 70 and 74 (FIG. 1) of the twist pin 50 are to beformed. The position of the wire established at step 724 locates theends 70 and 74 where the laser beam from the laser device 110 (FIGS. 6,7) will melt the wire to sever the fabricated twist pin and form theends 70 and 74.

[0122] The laser beam device 110 is actuated and the laser beam meltsthe wire at the end positions to sever the fabricated twist pin from thewire, as shown at step 728. The air flow from the venturi assembly 540(FIG. 7) conducts the severed and fabricated twist pin toward thecassette. Until all of the receptacles 118 of the cassette have beenfully occupied, twist pins will continue to be fabricated and deliveredto the cassette. Once all the receptacles of the cassette have beenoccupied, the program flow 700 stops at step 738.

[0123] In summary of the more detailed explanations of the improvementsdescribed above, numerous improvements are obtained by the bulge formingmechanism 106. A single bulge 58 (FIG. 1) is completely formed in asingle revolution of the rotating gripping assembly 292, therebyavoiding having to act twice on the strands to untwist them sufficientlyto form a single bulge, as was typical with prior art devices. Therotating clamp member 300, and the cam wheel 386 add a relatively smallamount of rotational inertia to the rotating gripping assembly 292,thereby allowing its rotational rate to be increased and theacceleration of the rotating gripping assembly 292 to be bettercontrolled and changed. Significant improvements in precision occur byavoiding the use of the complicated and massive clamping devices of theprior art. Such massive devices complicate and prevent adequate controlover the equipment and the wire when undergoing speed and accelerationchanges. The precise control over the rotational rate and the openingand closing of the clamping members 298 and 300 allows the wire to beadvanced precisely and under conditions which allow positioning of thebulges, the leader, the tail and the interval between bulges atpredetermined positions in the twist pin.

[0124] The improvements available from the bulge forming mechanism 106also achieve a higher production rate of twist pins. The rotatinggripping assembly 292 rotates continuously and fully creates a singlebulge during a continuous rotational interval of each completerevolution. During the remaining rotational interval of each revolution,the wire is advanced to allow the bulges to be fabricated sequentiallyand without lost motion and inefficiency. Advancing the wire from theslack wire S-shaped configuration 234 decouples the rotational inertiaof the spool 102 from the advancement of the wire into the bulge formingmechanism 106. Consequently, the wire is more quickly advanced into adesired position in the bulge forming mechanism 106 because it need notbe unwound against the resistance and inertia of the wire from the spool102. The speed at which the bulge forming mechanism 106 forms the bulgesneed not be reduced to accommodate latencies in advancing the wire.However in those cases where it is necessary to advance a greater amountof wire to form the leader of the twist pin, for example, the rotationalrate of the rotating gripping assembly can be slowed during the wireadvancing interval. More bulges are therefore created in a shorteramount of time, resulting in fabricating twist pins more efficiently andquickly.

[0125] Creating a single bulge as a result of a single revolutionachieves improvements over prior techniques requiring more than oneseparate movement to completely form the bulge. The shape of each bulgeformed is also more uniform, consistent and symmetrical as a result ofthe single bulge-forming movement. The crescent shaped gripping surfaces486 and 488 grip the wire strands in an oval shape to transfer a greateramount of rotational torque to rotate the wire in the anti-helicaldirection without slippage when forming the bulge. The shape of thebulges formed is enhanced by avoiding wire slippage. Consistent and moreuniformly shaped bulges create better electrical connections between thetwist pins and the vias of the printed circuit boards through which thetwist pins are inserted. The greater extent of the rotational intervalduring which the wire is untwisted in the anti-helical directioncontributes to the ability to form a single bulge during each revolutionof the rotating gripping assembly 292.

[0126] Forming each bulge as a single movement during a part of eachrevolution also contributes to forming the bulges concentrically andcoaxially along the length of the wire. Maintaining a coaxialrelationship of all the portions of the twist pin along the length ofthe twist pin assures that the twist pin will be more easily insertedthrough the aligned vias in the printed circuit boards. There is lesslikelihood that the wire will be deflected from a coaxial relationshipwhen the bulges are formed from a single continuous movement, comparedto the prior art technique of requiring more than one movement to formeach bulge.

[0127] The formation of the bulges in a continuous, non-reciprocatingoperation avoids the prior art problems associated with the latency andthe acceleration and deceleration forces created by the inertia and themass of various prior art mechanisms used to form the bulges. Instead,the bulges are formed as a result of continuous, motion-efficient andmore rapidly executed movements during which the wire is advanced,gripped, anti-helically rotated and released with each revolution of therotating gripping assembly.

[0128] A presently preferred embodiment of the invention and many of itsimprovements have been described with a degree of particularity. Thisdescription is of a preferred example of implementing the invention andis not necessarily intended to limit the scope of the invention. Thescope of the invention is defined by the following claims.

The invention claimed is:
 1. A bulge forming mechanism for formingbulges in a wire having helically coiled strands by untwisting thestrands in an anti-helical direction at a predetermined position to forman electrical connector from a segment of a length of the wire,comprising: a first gripping assembly including a first clamp member anda first actuator, the first clamp member moving to a closed position togrip the wire and prevent the wire from moving relative to the firstclamp member and to an open position in which the wire is free to moverelative to the first clamp member, the first actuator connected to thefirst clamp member to selectively move the first clamp member into theopen and closed positions; and a second gripping assembly including asecond clamp member and a second actuator, the second clamp membermoving to a closed position to grip the wire and prevent the wire frommoving relative to the second clamp member and to an open position inwhich the wire is free to move relative to the second clamp member, thesecond actuator connected to the second clamp member to selectively movethe first clamp member into the open and closed positions; and arotating carrier interconnecting the first and second grippingassemblies to rotate the first and second clamp members relative to oneanother in at least one complete relative revolution in a singlerelative rotational direction which is anti-helical relative to thestrands of the wire, the rotating carrier also positioning the first andsecond clamp members at a spaced apart location above and below thepredetermined location where a bulge is to be formed.
 2. A bulge formingmechanism as defined in claim 1 wherein: the first and second actuatorsclose the first and second clamp members during a relative rotationalinterval of greater than one-half of a complete relative revolution ofthe clamp members.
 3. A bulge forming mechanism as defined in claim 1wherein: the first and second actuators close the first and second clampmembers during a relative rotational interval of approximatelythree-fourths of a complete relative revolution of the clamp members. 4.A bulge forming mechanism as defined in claim 1 wherein: the first andsecond actuators open the first and second clamp members during arelative rotational interval of less than one-half of a completerelative revolution of the clamp members, the relative rotationalinterval when the first and second clamp members are in the openposition permits the wire to be advanced.
 5. A bulge forming mechanismas defined in claim 4 further comprising: a drive motor connected for arotating the rotating carrier; and the drive motor slows the relativerotation of the first and second gripping assemblies relative to oneanother during the relative rotational interval when the first andsecond clamp members are in the open position.
 6. A bulge formingmechanism as defined in claim 4 further comprising: a drive motorconnected for rotating the rotating carrier to achieve a relativerotational rate of the first and second gripping assemblies; and thedrive motor controls the relative rotational rate of the first andsecond gripping assemblies relative to one another during the relativerotational interval when the first and second clamp members are in theopen position to establish selective time intervals during which theclamp members occupy the open position.
 7. A bulge forming mechanism asdefined in claim 6 wherein: the drive motor establishes the time periodof the relative rotational interval when the first and second clampmembers are in the open position independently of the time period of therelative rotational interval when the first and second clamp members arein the closed position by controlling the relative rotational rate.
 8. Abulge forming mechanism as defined in claim 7 further in combinationwith a wire feeding mechanism which advances wire to the bulge formingmechanism during the relative rotational interval when the first andsecond clamp members are in the open position.
 9. A bulge formingmechanism as defined in claim 4 further in combination with a wirefeeding mechanism which advances wire to the bulge forming mechanismduring the relative rotational interval when the first and second clampmembers are in the open position.
 10. A bulge forming mechanism asdefined in claim 9 wherein the wire feeding mechanism advances the wireto the predetermined position where a bulge is to be formed in the wireby the bulge forming mechanism during the relative rotational intervalwhen the first and second clamp members are in the open position.
 11. Abulge forming mechanism as defined in claim 10 further in combinationwith a wire severing apparatus which severs the segment of the wire uponwhich the bulges have been formed from a remaining length of the wire,the wire feeding mechanism advancing the wire during the relativerotational interval when the first and second clamp members are in theopen position, the wire feeding mechanism advancing the wire to apredetermined position where it is to be severed after all of the bulgeshave been formed in the segment of the wire.
 12. A bulge formingmechanism as defined in claim 11 further comprising: a drive motorelectrically connected for a rotating the rotating carrier; and thedrive motor slows the relative rotation of the first and second grippingassemblies relative to one another during the relative rotationalinterval when the first and second clamp members are in the openposition.
 13. A bulge forming mechanism as defined in claim 12 wherein:the drive motor temporarily stops the relative rotation of the first andsecond gripping assemblies relative to one another during the relativerotational interval when the first and second clamp members are in theopen position.
 14. A bulge forming mechanism as defined in claim 1wherein: one of the first or second actuators is mechanically operated;and the other one of the first or second actuators is electricallyoperated.
 15. A bulge forming mechanism as defined in claim 14 furthercomprising: a sensor located to sense the operation of themechanically-operated actuator and to supply a signal upon the operationof the mechanically-operated actuator; and wherein: theelectrically-operated actuator is operated in response to the signalfrom the sensor.
 16. A bulge forming mechanism as defined in claim 1wherein: at least one of the first or second actuators is mechanicallyoperated.
 17. A bulge forming mechanism as defined in claim 1 wherein:At least one of the first or second actuators is electrically operated.18. A bulge forming mechanism as defined in claim 1 wherein: the firstand second actuators open the first and second clamp membersapproximately at the same time during a relative revolution of the clampmembers.
 19. A bulge forming mechanism as defined in claim 1 wherein:the first and second actuators close the first and second clamp membersapproximately at the same time during a relative revolution of the clampmembers.
 20. A bulge forming mechanism as defined in claim 1 wherein:the first gripping assembly is retained in a stationary position; andthe second gripping assembly is connected to the rotating carrier torotate in conjunction with the rotating carrier and relative to thefirst gripping assembly.
 21. A bulge forming mechanism as defined inclaim 20 further comprising: a drive motor connected for rotating therotating carrier in complete revolutions in a single rotationaldirection; and wherein: the second actuator is mechanically operated byrotation of the rotating carrier to move the second clamp member intoone of either the open or the closed positions at a predetermined pointin each revolution of the rotating carrier.
 22. A bulge formingmechanism as defined in claim 21 further comprising: a trip pin locatedadjacent to the rotating carrier; and wherein: the second actuatorincludes an actuating arm extending from the rotating carrier to contactthe trip pin during rotation of the rotating carrier to move the secondclamp member into one of either the open or the closed positions.
 23. Abulge forming mechanism as defined in claim 22 further comprising: asecond trip pin in addition to the trip pin first aforesaid; the secondtrip pin also located adjacent to the rotating carrier; and wherein: thesecond actuator includes a second actuating arm in addition to theactuating arm first aforesaid; the first actuator arm contacting thefirst trip pin to move the second clamp member into the open position;and the second actuating arm also extending from the rotating carrier tocontact the second trip pin during rotation of the rotating carrier, thesecond actuating arm contacting the second trip pin to move the secondclamp member into the closed position.
 24. A bulge forming mechanism asdefined in claim 23 wherein: at least one of the first or second trippins is located at a stationary position relative to the rotatingcarrier.
 25. A bulge forming mechanism as defined in claim 23 wherein:the rotating carrier comprises a carrier disk having a peripheral edge;the second actuator comprises a cam wheel positioned for rotationrelative to the carrier disk had a location adjacent to the peripheraledge of the carrier disk; and the cam wheel including the first andsecond actuator arms extending beyond the peripheral edge of the carrierdisk to contact the first and second trip pins, respectively, uponrotation of the cam wheel relative to the carrier disk.
 26. A bulgeforming mechanism as defined in claim 25 wherein: the second clampmember comprises at least one lever arm which moves the second clampmember between the open and closed positions when pivoted; and the camwheel further includes a surface which contacts the lever arm and pivotsthe lever arm upon rotation of the cam wheel.
 27. A bulge formingmechanism as defined in claim 25 wherein: the second clamp membercomprises a pair of separated lever arms which move the second clampmember between the open and closed positions when pivoted; the cam wheelis positioned between the separated lever arms and further includes acam surface which contacts the lever arms and pivots the lever arms uponrotation of the cam wheel as a result of one of the actuator armscontacting one of the trip pins.
 28. A bulge forming mechanism asdefined in claim 27 wherein: the second clamp member further comprisesone jaw member connected to one of the lever arms and one jaw memberconnected to the other lever arm, the jaw members contacting and holdingthe wire when the second clamp member is in the closed position;rotation of the cam wheel and the cam surface pivots the lever arms tomove the connected jaw members apart and toward one another to achievethe open and closed positions of the second clamp member, respectively;29. A bulge forming mechanism as defined in claim 28 wherein: each ofthe jaw members includes a contact surface which is crescent shaped. 30.A bulge forming mechanism as defined in claim 28 wherein: each of thejaw members includes a contact surface shaped to reposition the strandsof the wire when contacted and held into a cross-sectional configurationhaving a radial component upon movement of the second clamp member tothe closed position.
 31. A bulge forming mechanism as defined in claim28 wherein: each lever arm and the jaw member is formed from a sheet ofmaterial having a thickness; each jaw member includes a contact surfaceby which to contact and hold the wire; and the contact surface of eachof the jaw members is reduced in thickness relative to the thickness ofthe sheet of material to reduce a surface area of the contact surfacewhich contacts and holds the wire.
 32. A bulge forming mechanism asdefined in claim 28 wherein: the second clamp member is formed from asheet of spring tempered material; the spring tempered material createsresilient characteristics in the second clamp member; and the resilientcharacteristics normally force the lever arms toward one another to biasthe second clamp member to the closed position.
 33. A bulge formingmechanism as defined in claim 28 wherein: the second clamp memberfurther comprises an end portion to which the lever arms are connectedand from which the lever arms extend; the lever arms and end portion areintegrally formed from a sheet of spring tempered material; the springtempered material creates resilient characteristics in the second clampmember; and the end portion is connected to the carrier disk at aposition diametrically opposite from the location where the actuatorwheel is rotationally positioned on the carrier disk.
 34. A bulgeforming mechanism as defined in claim 33 wherein: the second clampmember further includes an arcuate portion which connects each lever armto the end portion; the resilient characteristics of the lever arms, thearcuate portions and the end portion normally force the lever armstoward one another to bias the jaw members apart the second clamp memberto the closed position; and the rotation of the cam wheel causes the camsurface of the cam wheel to force the lever arms apart from one anotheragainst the force of the resilient characteristics of the second clampmember.
 35. A bulge forming mechanism as defined in claim 28 wherein:the rotating carrier rotates about an axis of rotation; the contactsurfaces of the jaw members of the second clamp member are positionedconcentrically about an axis of rotation of the rotating carrier; andthe rotating carrier includes a hole located at the axis of rotationthrough which the wire extends.
 36. A bulge forming mechanism as definedin claim 22 further comprising: a sensor located adjacent to the trippin to sense the contact of the actuating arm with the trip pin and tosupply a signal upon such contact; and wherein: the first actuator isoperated in response to the signal from the sensor.
 37. A bulge formingmechanism as defined in claim 21 wherein: the drive motor is a steppermotor.
 38. A bulge forming mechanism as defined in claim 20 wherein: thefirst clamp member comprises an arm which pivots when the first clampmember moves between the open and closed positions; and the firstactuator is connected to the arm to pivot the arm.
 39. A bulge formingmechanism as defined in claim 38 wherein: the first actuator comprises asolenoid.
 40. A bulge forming mechanism as defined in claim 38 wherein:the first clamp member further comprises a base with respect to whichthe arm pivots when the first clamp member moves between the open andclosed positions; the first clamp member further comprises one jawmember connected to the arm and one jaw member connected to the base,the jaw members contacting and holding the wire when the first clampmember is in the closed position.
 41. A bulge forming mechanism asdefined in claim 40 wherein: each of the jaw members includes a contactsurface which is semicircular shaped.
 42. A bulge forming mechanism asdefined in claim 41 wherein: the arm and the base are formed from asheet of material having a thickness; each jaw member includes a contactsurface by which to contact and hold the wire; and the contact surfaceof each of the jaw members approximately the same thickness as thethickness of the sheet of material from which the arm and base areformed.
 43. A bulge forming mechanism as defined in claim 40 wherein:the first clamp member is formed from a sheet of spring temperedmaterial; the spring tempered material creates resilient characteristicsin the first clamp member; and the resilient characteristics normallyforce the jaw member on the arm away from the jaw member on the base tobias the first clamp member to the open position.
 44. A bulge formingmechanism as defined in claim 43 wherein: the first actuator comprises asolenoid having a plunger; the plunger is connected to the arm; and theplunger is moved by actuating the solenoid to pivot the jaw member onthe arm toward the jaw member on the base and to overcome the bias ofthe resilient characteristics of the first clamp member.
 45. A bulgeforming mechanism as defined in claim 44 wherein: the first clamp memberfurther includes an arcuate portion which connects the arm to the base;the resilient characteristics of the arm, the base and the arcuateportion normally bias the jaw members on the arm away from the jawmembers on the base portion.
 46. A bulge forming mechanism as defined inclaim 45 wherein: the arcuate portion extends in a semicircular curve toconnect the arm to the base.
 47. A bulge forming mechanism as defined inclaim 40 wherein: the rotating carrier rotates about an axis ofrotation; each jaw member includes a contact surface by which to contactand hold the wire; and the contact surfaces of the jaw members arepositioned concentrically about an axis of rotation of the rotatingcarrier when the first clamp member is moved to the closed position. 48.A bulge forming mechanism as defined in claim 47 wherein: the contactsurface of the jaw member on the base remains concentrically positionedabout the axis of rotation of the rotating carrier when the first clampmember is moved to the open position.
 49. A bulge forming mechanism asdefined in claim 1 wherein: at least one of the first or second clampmembers further comprises jaw members which contact and hold the wirewhen the first and second clamp member are in the closed positions; andthe jaw members of at least one of the first or second clamp membersincludes a contact surface shaped to reposition the strands of the wirewhen contacted and held into a cross-sectional configuration having aradial component upon movement of the one clamp member to the closedposition.
 50. A bulge forming mechanism as defined in claim 49 wherein:the contact surface of the jaw members of the one clamp member arecrescent shaped.
 51. A method of forming bulges in a wire havinghelically coiled strands by untwisting the strands in an anti-helicaldirection at a predetermined position to form an electrical connectorfrom a length of the wire, comprising the steps of: gripping the wirewith a first clamp member and preventing the wire from moving relativeto the first clamp member by moving the first clamp member to a closedposition; gripping the wire with a second clamp member and preventingthe wire from moving relative to the second clamp member by moving thesecond clamp member to a closed position; positioning the first andsecond clamp members at a spaced apart location above and below thepredetermined location where a bulge is to be formed. rotating the firstand second clamp members relative to one another in at least onecomplete relative revolution in a relative rotational direction which isanti-helical relative to the strands of the wire; and moving both thefirst and second clamp members to the closed position during a relativerotational interval of greater than one-half of a complete relativerevolution of the clamp members.
 52. A method as defined in claim 51further comprising the step of: moving both the first and second clampmembers to the closed position during a relative rotational interval ofapproximately three-fourths of a complete relative revolution of theclamp members.
 53. A method as defined in claim 51 further comprisingthe step of: releasing the grip on the wire by the first clamp memberand allowing the wire to move relative to the first clamp member bymoving the first clamp member to an open position; releasing the grip onthe wire by the second clamp member and allowing the wire to moverelative to the second clamp member by moving the second clamp member toan open position; moving both the first and second clamp members to theopen position during a relative rotational interval of less thanone-half of a complete relative revolution of the clamp members.
 54. Amethod as defined in claim 53 further comprising the step of: advancingthe wire longitudinally relative to the first and second clamp memberswhen the first and second clamp members are moved to the open position.55. A method as defined in claim 54 further comprising the step of:advancing the wire longitudinally to another predetermined position atwhich a bulge is to be formed after having formed a previous bulge. 56.A method as defined in claim 54 further comprising the step of: slowingthe relative rotation of the first and second clamp members relative toone another during the relative rotational interval when the first andsecond clamp members are in the open position.
 57. A method as definedin claim 54 further comprising the step of: temporarily stopping therelative rotation of the first and second clamp members relative to oneanother during the relative rotational interval when the first andsecond clamp members are in the open position.
 58. A method as definedin claim 54 further comprising the step of: controlling the relativerotational rate of the first and second gripping assemblies relative toone another during the relative rotational interval when the first andsecond clamp members are in the open position to establish selectivetime intervals during which the clamp members occupy the open position.59. A method as defined in claim 53 further comprising the steps of:establishing the time period of the relative rotational interval whenthe first and second clamp members are in the open positionindependently of the time period of the relative rotational intervalwhen the first and second clamp members are in the closed position bycontrolling the relative rotational rate of the first and second clampmembers.
 60. A method as defined in claim 53 further comprising thesteps of: advancing the wire during the relative rotational intervalwhen the first and second clamp members are in the open position to apredetermined position where the wire is to be severed after all of thebulges have been formed in the segment of the wire; and severing thewire to separate the segment from the remaining length of wire.
 61. Amethod as defined in claim 51 further comprising the step of: moving thefirst and second clamp members to the open position at approximately atthe same time during a relative revolution of the clamp members.
 62. Amethod as defined in claim 51 further comprising the step of: the firstand second actuators close the first and second clamp membersapproximately at the same time during a relative revolution of the clampmembers.
 63. A method as defined in claim 51 further comprising the stepof: retaining the first clamp member a stationary position; and rotatingthe second clamp member relative to the first clamp member.
 64. A methodas defined in claim 63 further comprising the steps of: rotating thesecond clamp member in complete revolutions in a single rotationaldirection; and moving the second clamp member to the open position at afirst predetermined point in each revolution of the second clamp member.65. A method as defined in claim 64 further comprising the step of:moving the second clamp member to the closed position at a secondpredetermined point in each revolution of the second clamp member, thefirst and second predetermined points being different from one another.66. A method as defined in claim 51 further comprising the step of:gripping the wire by repositioning the strands of the wire into across-sectional configuration having a radial component by moving one ofthe first or clamp members to the closed position.
 67. A method asdefined in claim 51 further comprising the step of: moving one of theclamp members to the closed position by force overcoming resilientspring characteristics which normally bias the one clamp member to theopen position.
 68. A method as defined in claim 51 further comprisingthe step of: moving one of the clamp members to the open position byforce overcoming resilient spring characteristics which normally biasthe one clamp member to the closed position.